电絮凝中zeta电位和粒径的讨论

Desalination204(2007)33–38PresentedatEuroMed2006conferenceonDesalinationStrategiesinSouthMediterraneanCountries:CooperationbetweenMediterraneanCountriesofEuropeandtheSouthernRimoftheMediterranean.SponsoredbytheEuropeanDesalinationSocietyandtheUniversityofMontpellierII,Montpellier,France,21–25May2006.*Correspondingauthor.Electroflocculation:theeffectofzeta-potentialonparticlesizeE.Ofira*,Y.Orenb,A.AdinaaDivisionSoilandWaterSciences,FacultyofAgricultural,FoodandEnvironmentalQualitySciences,TheHebrewUniversityofJerusalem,13Nof-HarimSt.,Jerusalem96190,IsraelTel.+972(52)8795-955;Fax[phone];email:[e-mail]earch,BenGurionUniversity,P.O.B653,BeerSheva84105,IsraelReceived2January2006;accepted27March2006AbstractElectroflocculation(EF)ofwastewaterorwaterforreusewithcolloidalparticles,suchaskaolinandironwiththerightpH,mightbeoptimalforaggregationduringwatertreatment.Inthispaper,theEFprocesswascomparedtochemicalflocculation(CF)throughζ-potentialandparticlesizeparameters.Theresultsdemonstratethattheparticlebecamelarger,exceptinthecaseofpH4,where,after50minofflocculation,therewasajumpinthevalueandtheparticleattainedadiameterofmorethan800nm.Throughouttheentireflocculationtime,theζ-potentialvaluesindicatedastrongernegativechargeontheparticle.Basically,therewasagradualriseinabsoluteζ-potentialwiththeincreaseinparticlesize.Thereasonforthisbehaviorcanbeexplainedbythesolubilityofkaolinwithadecreasingionicstrength,whencertainironionsarereleasedfromtheelectrodeandthechargeoftheparticleisaltered.Theaggregationprocess,wherebyafewsmallparticleswithanegatively-chargedsurfacearerenderedintoalarger-sizedparticle,resultsinalargertotalnegativecharge.Ithaslongbeenrecognizedthatζ-potentialisaverygoodindexofthemagnitudeoftherepulsiveinteractionbetweencolloidalparticles.Measurementsofζ-potentialarecommonlyusedtoassessthestabilityofcolloidalandparticlesizeproducedbyEF.Thus,thecouplingoftheEFofkaolinandironwiththerightpHmightbeoptimalforproducingparticles.Keywords:ζ-potential;Particlesize;Wastewatertreatment;Chemicaltreatment;Flocculation;Electroflocculation0011-9164/07/$–Seefrontmatter©2006ElsevierB.V.Allrightsreserved.doi:10.1016/j.desal.2006.03.53334E.Ofiretal./Desalination204(2007)33–381.IntroductionThedeterminationoftherheologicalcharac-teristicsofclay(kaolin)–iron–watersuspensionsexhibitsverysignificantpropertiesduetoaggrega-tionundervaryingconditions.EFasCFisaco-agulationprocessinvolvingtheinsitugenerationofions(coagulants)bytheelectrolyticoxidationofanappropriateanodematerialorfromchem-icals[1,2].Thisprocesscreateschemicalandphy-sicalconditionsfortheseparationofthecolloidsinwasteorcontaminatedwaterforreuse,whereahighnegativechargeisusual[3].Theavailabilityofreproduciblecolloidsys-temsandanintegratedapproachtothestudyofsurfacepropertieshavegivenusmoreconfidenceinEF’svalueasacharacterizingparameter[4].Thestabilityofacolloidalparticleisdeterminedbythebalancebetweentherepulsiveandattractiveforcesthattheparticlesexperienceastheyap-proacheachother.Theζ-potentialdecreasesandaquitesharplydefinedcoagulationconcentrationcanbeidentified[5,6].Thisisthepointatwhichthepotentialenergybarrieropposingcoagulationdisappears,anditiscalledthecriticalcoagulationconcentration(c.c.c.)[7].Anestimationofthec.c.c.canbeobtainedbyusinganapproximateexpressionforthepotentialenergyofattractionandthepotentialenergyofrepulsion.Anempiricalrelationbetweenζ-potentialandcoagulationbehaviorwasfirstprovidedbyEilersandKorff[8]usingpublisheddataonavarietyofsystems[2,9].TheoreticaljustificationwasprovidedbyDerjaguin[10,11]onthebasisoftheDebye–Huckelapproximation.Assumingthatζ-potentialmeasuresthepotentialcharacterizingthediffusepartofthedoublelayer,itishardlysurprisingthatitshouldprovideagooddescriptionoftheco-agulationprocess,sinceitisthediffuselayerpo-tentialsthatareinvolvedindouble-layeroverlap.Amuchmoreexactingtestoftheuseofζ-potentialtocharacterizecoagulationbehaviorwouldre-quirenotmerelyacorrelationwiththec.c.c.,whererapid(i.e.,particlediffusionrate)controlledcoagulationbegins,butratheranunderstandingoftheregionofslowcoagulation[12].Thescopeofthispresentstudyistoexaminetheeffectofflocculationonironandkaolinsolutionswhileexaminingthecorrelationbetweenζ-potentialandparticlesizeduringEF.2.MaterialsandmethodsAlargenumberofsamplesofcalibratedwater,preparedinthelaboratorywereusedinthisstudy.Ferricchloride(FeCl3·6H2O),whichservedasachemicalcoagulantproducedbyMerckatmini-mum99%purity,wasusedforsynthesiswithotherimpuritiessuchassulfate,Pbandzinc(lessthan0.005%each)andnitrogencompositions(lessthan0.01%).InEF,Fe3+ionsgeneratedbyelectrolyticoxidationfromanSAE1020steelelectrodewereusedascoagulantandwereaddedtosixcups,800mleach,ofcalibratedwater(Fig.1).Thecalib-ratedwaterwastapwaterthatunderwentafewstagesofpurification:50-micronfiltrationandreverseosmosistrueMWCO(KDa),UF-PA50H,hydrophilicmembranefrompolyaramid(PA)withpermeabilityof570(l/h.m.bar)at20ºC.ThewaterwasthenpassedthroughapolishermadefromamixtureofemberlitIR120andIRA400.InEF,sodiumnitratewas